Back around 1978, my wife and I bought an old Fiat 124 sedan. It was at the owner's house and the battery was dead. I disconnected the battery terminals and connected the jumper cables from our car directly to the battery terminals and the car started.
After the Fiat was started, I connected the cables back to the dead battery, and I could tell the Fiat's system suddenly had a heavy load on it but continued to run.
It was starting to get dark and I got the Fiat home as quickly as possible without turning on lights, radio, etc.
Made it home fine and got a new battery the next day.

My questions are:
can modern cars be started this way?
Will it damage the electrical/electronic system?

1 Answer
1

I can be started that way, but I wouldn't advise it. The issue is leaving the car running while reconnecting the battery cables. You run the risk of damaging the alternator if one of the "jumper" clamps slips off.